Conventionally, in order to obtain a modified polymer compound by hydrolyzing a hydrolyzable group in a side chain of a polymer compound or newly bonding an addition reaction product to a main chain or a side chain, for example, methods for hydrolysis reaction and dehydration condensation reaction in the presence of an acidic catalyst or an alkaline catalyst have been employed.
For example, a large quantity of poly(vinyl alcohol) has been used as a raw material of alkylacetalized poly(vinyl alcohol) (hereinafter, also referred to as poly(vinyl acetal) resin) to be used as an intermediate film for laminated glass, an emulsifier, a molded product and an adhesive for various purposes. Poly(vinyl alcohol) is generally synthesized by saponification of poly(vinyl acetate) in the presence of an acidic catalyst or an alkaline catalyst.
The quality of poly(vinyl alcohol) is determined mainly based on the polymerization degree, the polymerization degree distribution, the saponification degree, the saponification degree distribution and the purity so-called pure component. In particular, the saponification degree and the pure component are particularly important and, depending on their values, problems that no intended property is obtained and that the property is deteriorated with the lapse of time may possibly occur. However, the saponification degree and the pure component of poly(vinyl alcohol) are in trade-off relation each other and, in order to improve the pure component, the amount of the acidic catalyst or the alkaline catalyst has to be decreased. Therefore, the desired saponification degree cannot be obtained to result in easy coloration of a product or it takes a long time for saponification to forcibly increase the saponification degree. Further, in order to remove the catalyst upon completion of the saponification reaction, the product compounds are commonly washed with a large quantity of water. However, it results in difficulty of increasing the product yield.
The poly(vinyl acetal) resin has been used for various purposes, for example, intermediate films for laminated glass, a wash primer for metal treatment, a variety of coating materials, adhesives, resin processing agents, and ceramic binders. Especially, laminated glass having an intermediate film made of the poly(vinyl acetal) resin is excellent in impact energy absorption property, transparency, and adhesion property to glass and is highly safe since fragments are not scattered at the time of break, so that the laminated glass has been used widely as window glass of traffic vehicles such as automobiles, window glass of buildings and the like. As described in Japanese Kokai Publication Hei-6-1853, the poly(vinyl acetal) resin is generally synthesized by dehydration condensation of poly(vinyl alcohol) and aldehyde in the presence of an acidic catalyst.
The acetalization degree and the purity of the obtained poly(vinyl acetal) resin greatly affect the properties of intermediate films of the poly(vinyl acetal) resin. That is, in the case where the purity of the poly(vinyl acetal) resin is low, it becomes impossible to obtain any intermediate film of the poly(vinyl acetal) resin having intended properties. Therefore, at the time of producing the poly(vinyl acetal) resin from poly(vinyl alcohol) by using an acidic catalyst, in order to increase the purity, washing with a large quantity of water is required and it results in low productivity.
To deal with such problems, method for producing modified polymer compounds without using any acidic catalyst or alkaline catalyst has been-studied. For example, a method for modifying polymers at the time of extrusion molding of polymer compounds has been studied. It is a method for supplying a polymer compound together with a reactive monomer and a peroxide (a radical generating agent) to an extrusion molding apparatus to generate radical in the extrusion molding apparatus, thereby grafting polymers. However, with the method, the reaction system cannot be controlled since the reaction is promoted with the radical. Decomposition reaction of the main chain of the polymer compound is caused simultaneously with the grafting reaction to lead to problems such as decrease of the polymerization degree of the polymer compound or production of homopolymers of the reactive monomer as byproducts.